The noradrenergic innervation of the vasa nervorum in old rats: a fluorescence histochemical study

Age-related changes in catecholaminergic nerve fibers of rat heart and coronary vessels

BACKGROUND

Age-related changes of catecholaminergic nerve fibers supplying the myocardium and the coronary vessels were studied in adult and in old rats.

OBJECTIVE

The purpose of this study was to investigate whether there are quantitative changes in myocardial and/or coronary catecholaminergic nerve fibers and related neurotransmitters.

METHODS

Samples of myocardium and/or coronary vessels were studied by means of glyoxylic acid induced fluorescence, aldehyde-induced fluorescence, and neuropeptide Y immunoreactivity. All morphological results were submitted to quantitative analysis of images. Biochemical dosage of proteins and of norepinephrine was also performed, and morphological data were compared with biochemical ones. Finally, all data were subjected to statistical analysis.

RESULTS

Our findings are indicative of an age-related decrease of all types of fluorescent sympathetic nerve fibers in rat heart and coronary arteries. Moreover, our data show that aging induces a strong decrease of norepinephrine levels in tissue homogenates of rat heart and coronary vessels. The majority of the catecholaminergic nerve fibers that show strong age-related changes are not contiguous with contractile cells of myocardium and/or of vascular wall. In fact, these fibers are located in adventitial (or epicardial) and in endothelial (or endocardial) layers.

CONCLUSION

The decrease of the catecholaminergic innervation of heart and coronary vessels of old rats can be in close relationships to the poor cardiac and/or coronary functions observed in old animals.

Innervation of normal human sural and optic nerves by noradrenaline- and peptide-containing nervi vasorum and nervorum: effect of diabetes and alcoholism

Histochemical, immunohistochemical and neurochemical techniques were used to examine the innervation of epineurial nerve sheaths and fascicular nerve bundles of human sural and optic nerves from controls and patients with peripheral neuropathy due to diabetes or alcoholism. The normal distribution of autonomic nerves in both nerve trunk sheaths consisted of a dense innervation by noradrenaline (NA)-containing nerves of the vasa nervorum, together with some fibres in the nervi nervorum. Intrafascicular NA-containing nerves were only present in the sural nerve. Vasoactive intestinal polypeptide (VIP)- and neuropeptide Y (NPY)-containing nerves also innervated the vasa nervorum and nervi nervorum of the nerve sheaths, although their density was considerably less. Substance P (SP)-containing nerves were sparse and primarily intrafascicular. Neurochemical assays for NA, VIP, NPY and SP in fascicular and epineurial preparations from the sural and optic nerves confirmed the light microscopical observations. Post mortem delay significantly affected the NA levels in the sural nerve but not in the optic nerve while the NA fascicular/epineurial ratio for the sural nerve was independent of this factor. Age, sex and the presence of alcohol at time of death had no effect on transmitter levels in normal sural nerves. In the optic nerve fascicles NA levels were higher in females than in males. In patients with peripheral neuropathy there was a significant reduction in the SP fascicular/epineurial ratio in both the optic nerve, which was histologically normal, and in the sural nerve, where there was evidence of neuropathy. The NA fascicular/epineurial ratio was also significantly reduced in the sural nerve from patients with peripheral neuropathy with a possible greater effect in diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased density of beta-adrenergic and muscarinic cholinergic receptor sites in the vasa nervorum of aged rats

The pharmacological profile and the anatomical localization of beta-adrenergic and muscarinic cholinergic receptors of the vasa nervorum were studied in sections of sciatic nerve using radioreceptor binding and light microscope autoradiography techniques. Sprague-Dawley rats of 4 and 24 months of age were used. [3H]Dihydroalprenolol (DHA) and [3H]quinuclidinyl benzilate (QNB) were used to label beta-adrenergic and muscarinic cholinergic receptors, respectively. The ligands were bound to sections of rat sciatic nerve in a manner consistent with the labelling of beta-adrenergic or muscarinic cholinergic receptors in the 2 age groups investigated. The dissociation constant (Kd) values (about 1.37 nM for [3H]DHA and 0.75 nM for [3H]QNB) did not significantly change between 4- and 24-month-old rats. The maximum concentration of binding sites (Bmax) for [3H]DHA was decreased by about 35% in 24 in comparison with 4-month-old rats. The Bmax value for [3H]QNB was reduced by about 50% in the aged rats. Light microscope autoradiography revealed the development of specific silver grains in the medial layer of epineurial and perineurial arteries in sections of sciatic nerve exposed either to [3H]DHA or [3H]QNB. The number of silver grains developed in epineurial and perineurial arteries of rats of 24 months is significantly lower than in animals of 4 months. The above results suggest the occurrence of an age-dependent loss in the density of beta-adrenergic and muscarinic cholinergic receptors of vasa nervorum. Vasa nervorum are the blood vessels which supply peripheral nerve trunks. They are constituted by outer (epineurial) and inner (perineurial) arteries and veins as well as by a capillary (endoneurial) plexus. Vasa nervorum are innervated by both sympathetic and non-sympathetic nerves which probably play a role in the pathogenesis of some neuropathies. Several different neurotransmitter containing nerve fibres have been identified in the vasa nervorum perivascular plexuses. However, no information is so far available concerning the neurotransmitter receptors of vasa nervorum. Moreover, although the occurrence of age-dependent changes in peripheral nerve morphology and function is well documented, very few reports were centered on the age-dependent changes of the vasa nervorum. The aims of the present study were to characterize pharmacologically and to localize anatomically the beta-adrenergic and muscarinic cholinergic receptors in the rat vasa nervorum. Moreover, the effect of ageing on the density and pattern of these receptors was investigated.

Adrenergic innervation of the tibial and vagus nerves in rats of different ages

Adrenergic nerve fibers innervating blood vessels in the epi-perineurium and endoneurium of the tibial and vagus nerves of male Fischer-344 rats of different ages were examined using formaldehyde-induced fluorescence technique and fluorescence microscopy. Between 6 and 24 months of age, no significant difference in the mean density of perivascular innervation in the epi-perineurium of the nerves was found, whereas between 24 months and 30 months the density decreased in both nerve types. The intensity of noradrenaline fluorescence of nerve fibers also was decreased in the oldest age group. In the endoneurium, the density of adrenergic nerve fibers was reduced by 57% at 24 months, and by more than 98% at 30 months as compared with 18 months. Age-related differences were similar in the tibial and vagus nerves. The results suggest that adrenergic neuronal control of the microcirculation in the rat tibial and vagus nerves is lost during aging as it is in other organs of the cardiovascular system.

Age-related changes of noradrenergic innervation of rat splanchnic blood vessels: a histofluorescence and neurochemical study

The influence of ageing on the noradrenergic innervation of superior mesenteric artery and vein, renal artery and vein, and portal vein was studied in male Wistar rats by means of catecholamine histofluorescence, image analysis techniques and high pressure chromatography with electrochemical detection. Old age was accompanied by a marked increase in the density of noradrenergic innervation and an increase of noradrenaline levels in superior mesenteric artery, renal artery, and portal vein. In contrast, no significant age-related changes were observed in the density of noradrenergic innervation or in noradrenaline levels in superior mesenteric and renal vein. The present data indicate that, at least in superior mesenteric and renal artery and portal vein, senescence is not accompanied by loss or by lack of change in the noradrenergic innervation as commonly believed to be the case in many vascular trees. On the basis of our findings it cannot be excluded that increased plasma catecholamine levels observed in senescence derive, in part, from perivascular sympathetic endings.

Increase in substance P levels in the lung of old rats

Substance P levels in the lung of young (3-month-old), adult (12-month-old), senescent (20-month-old) and aged (28-month-old) male Wistar rats were determined by radioimmunoassay. Levels of substance P were constant until 28 months of age when these become significantly higher (approximately more than 2 times, p less than 0.001) than the values found in younger rats. Whether the increase of substance P content in the lung of old rats may reflect changes in the density of substance P containing nerve fibres or in the content of the peptide in single nerve fibres is discussed.

Age-related changes in the noradrenergic innervation of the coronary arteries in old rats: a fluorescent histochemical study

Age-related changes in the density of the noradrenergic perivascular plexus supplying the coronary vessels in the rat were studied using the glyoxylic acid fluorescence technique. A marked decrease in the density of the noradrenergic innervation of large, medium and small size coronary arteries was observed in 25-month-old rats. In contrast, the fluorescent nerves supplying the coronary veins were not decreased in old animals. The present data are indicative of an age-related reduction of fluorescent noradrenergic nerves in the rat coronary arteries.